1. Field of the Invention
The present invention relates to a method and apparatus for realizing an optical multiplexer/demultiplexer, and more particularly, to an optical multi-Dlexer/demultiplexer having a continuous interferometer filter with a single .lambda./2 dielectric layer.
2. Description of the Art
While fiber optic technology has been recognized as having a large transmission capacity, there remains the issue of increasing the utilization of the bandwidth making up that capacity. Greater bandwidth utilization is necessary as the demand for greater amounts of data transmission, both telephonically and over the Internet, increases for such things as, inter alia, speech and video images and graphics. In an attempt to allow for greater bandwidth utilization over a fiber optic cable, different types of wavelength division multiplexers/demultiplexers (WDM) have been implemented. Most of the WDM's implemented have a number of filters, each tuned to a different waveband. These multi-filter types of WDM's, however, are expensive and cumbersome as each waveband to be utilized in the fiber optic cable must have its own filter. Alternatively, a few attempts have been made to implement WDM's utilizing only one single filter for all of the wavebands.
For example, in U.S. Pat. No. 5,781,341, issued Jul. 14, 1998, to Lee, a WDM is presented having a single tunable optical filter for waveband selection. The filter is tunable in that it is capable of changing direction with respect to an angle of incidence of an incoming beam of light. Such change in direction of the filter is effected by a motor mechanism. The motor mechanism, however, Las many moving parts and thus may be expensive to manufacture and may be subject to frequent breakage. Further, since tunability of the filter is dependent upon its ability to be adjustably moved by the motor mechanism, if there is a breakage the filter is no longer tunable.
Another example, U.S. Pat. No. 5,481,402, issued Jan. 2, 1996, to Cheng et al., also presents a WDM having a single tunable optical filter for waveband selection. In this patent, the filter is tunable in that it is capable of pivoting around a pivot axis, thus changing the passband of the filter in accordance with the angle of incidence. The pivot effect of the filter is effected by a rotating adjustment arm. Again, however, tile moving parts of the filter arrangement may be expensive to manufacture and may be subject to breakage. And also again, since tunability of the filter is dependent upon its ability to be adjustably moved by the rotating adjustment arm, if there is a breakage the filter is no longer tunable.
Yet another example, U.S. Pat. No. 4,671,603, issued Jun. 9, 1987, to McQuoid et al., also presents a WDM having a single tunable filter. However, instead of a filter which is tunable by physical movement, the filter is constructed having differing refractive index layers stacked upon each other for the length of the filter. The differing refractive index layers make the filter tunable in that wavelength selectivity is dependent upon the angle at which the light beam strikes the filter, relative to the original angle of incidence of the light beam. While tunable, the filter may be expensive to manufacture as the filter must have individual layers of differing refractive indexes along its entire length. Further, reflective mirrors, placed on either side of the filter, are needed to redirect the light beam back towards the filter.
Thus, while attempts have been made to present a WDM having only a single filter, none have yet been developed that are easily implemented and inexpensive.